The present invention relates to a liquid ejection apparatus and a driving method thereof.
Heretofore, in general, as a liquid ejection apparatus for ejecting a liquid from a nozzle toward a target, an ink jet recording apparatus has been widely used. This ink jet recording apparatus comprises a carriage and a recording head mounted on the carriage. While moving the carriage on the recording head, the apparatus ejects ink from the nozzle formed on the recording head and performs printing on a recording medium.
Such an ink jet recording apparatus, when not being operated, often suffers an increase in viscosity of the ink in the nozzle and solidification of the ink because of evaporation of the ink solvent, such as water vapor and the like from the nozzle of the recording head. As a result, there is the possibility of poor performance of the printing, such as dust deposition on the nozzle and poor ink ejection.
To solve these problems, an ink jet recording apparatus comprising capping means has been known. In more detail, the capping means comprises a cap capable of covering the nozzle surface of the recording head and a suction pump capable of depressurizing the inside of the cap. When not being operated, the nozzle surface of the recording head is covered by this cap with humidity in the space formed by the recording head and the cap being maintained, thereby preventing the ink from being solidified.
Moreover, the depressurization of the inside of the cap by the suction pump in a state of covering the nozzle surface of the recording head by the cap allows ink, dust and the like to be drawn from the nozzle. This protects the ink from increased viscosity, dust and the like in the vicinity of the nozzle, thereby making it possible to maintain the performance of the nozzle in an optimum state.
In the ink jet recording apparatus as described above, there are often cases where bubbles and impurities mixed in the ink are stagnated in the ink flow path from an ink cartridge to the recording head. Because of these bubbles and impurities, it is feared that the ink filling factor in the ink flow path is reduced, supply property of the ink to the recording head is reduced, bubbles and impurities flow out of the nozzle during printing, and printing quality is reduced.
Hence, to increase the ink filling factor in the ink flow path, an ink jet recording apparatus comprising a valve unit, which is a “choke valve”, has been known (for example, see Japanese Laid-Open Patent Application Publication No. 2001-38925). To describe it in detail, this valve unit is provided in the ink flow path between an ink cartridge and the recording head, and is capable of opening and closing the ink flow path.
By putting the valve unit into a closed state, and covering the nozzle surface of the recording by the cap, and depressurizing the inside of the cap by suction means, a negative pressure accumulates within the ink flow path in a section downstream from the valve unit. After that, by putting the valve unit into an open state while the negative pressure is in an accumulated state, the flow speed of the ink in the ink flow path is increased instantaneously. Thus, “choke cleaning” is performed, which discharges from the nozzle the bubbles and impurities stagnated together with the ink flow speed sped up instantaneously. As a result, it is possible to increase the filling factor of the ink in the ink flow path.
More specifically, as shown in FIG. 51(a), the inkjet recording apparatus described in Japanese Laid-Open Patent Publication No. 2001-38925 includes a valve device 403 arranged between the recording head 401 and the ink cartridge 402. The recording head 401 is connected to a lower end portion of the valve device 403. A passage 401a defined in the recording head 401 thus communicates with a passage 403a defined in the valve device 403. An ink supply needle 404 is formed at an upper end portion of the valve device 403 and communicates with the passage 403a. An ink cartridge 402 is connected to the ink supply needle 404. Ink is supplied from the ink cartridge 402 to a passage 401b defined in the recording head 401 via the ink supply needle 404 and the passage 403a. The ink is then ejected from nozzles 401b of the recording head 401. Further, a columnar shaft 405 is rotatably passed through the valve device 403 in such a manner as to cross the passage 403a from a side surface of the valve device 403. The shaft 405 includes a communication hole 405a communicating with the passage 403a. As illustrated in FIG. 51(b), the shaft 405 disconnects the communication hole 405a from the passage 403a when being rotated. The supply of the ink to the recording head 401 is thus blocked.
When the above-described cleaning operation is performed, the shaft 405 is rotated for stopping the ink supply to the recording head 401. Further, the nozzles 401b are sealed by a capping member 406 and negative pressure is applied from a non-illustrated suction pump to the nozzles 401b through the capping member 406. When the negative pressure is accumulated on the nozzles 401b, the shaft 405 is rotated in such a manner as to resume the ink supply to the recording head 401, as shown in FIG. 51(a). As a result, the accumulated negative pressure causes the ink to be rapidly ejected from the nozzles 401b of the recording head 401. At this stage, the bubbles and impurities trapped in the passages 401a, 403a are ejected from the nozzles 401b, together with the ink.
Incidentally, the valve unit disclosed in the above publication is configured such that the switching of its valve opening and closing is usually performed by an actuator and the like. Consequently, it is necessary not only to perform the drive control for the cap and the absorption pump, but also to perform the drive control for the actuator of the valve unit, which is a cause of making the control complicated. Further, there is a need to consider arrangement of space for the actuator, and this can increase the size of the apparatus.
The present invention has been made in view of the above-described problems, and an objective of the invention is to provide a liquid ejection apparatus and a driving method thereof, which is capable of choke cleaning with simple control without increasing the size of the size of the apparatus.